Introduction to Wind Tunnel

The basic concept and surgical procedure of subsonic bakshis tunnel was exhibit in this test by conducting reign surface pinch analysis on a NACA 0015 aerofoil. The small subsonic land up tunnel along with apparatus such as, the manometer lurch, the abandoned manometer and the pitot smooth tube were used with different baffle slewtings to record varying contract readings. To achieve this objective, some assumptions were made for the lower range of subsonic flow to simplify the overall analysis.From the obtained aerodynamic measurements u unrighteousnessg a pitot-static tube mounted ahead of the airfoil at the test section, the actual pep pill was determined and by relating it to the theoretical speeding, the velocity coefficient was measured. The velocity coefficient varies for each baffle setting by a factor of decimals, so the velocity coefficient can be used as a correction factor. Further, the coefficients of drag were deliberate for the by-line angles of good time, 10o, 15o, and 20o and were compared with the published set. INTRODUCTIONThe wind tunnel is an absolute necessity to the development of modern aircrafts, as today, no manufacturing business delivers the final product, which in this case can be civilian aircrafts, military aircrafts, missiles, spacecraft, and automobiles without measuring its lift and drag properties and its stability and controllability in a wind tunnel. Benjamin Robins (1707-1751), an English mathematician, who first employed a swirl arm to his machine, which had 4 feet long arms and it, spun by falling weight acting on a pulley however, the arm tip reached velocities of only few feet per second. 4 Figure 1 Forces exerted on the airfoil by the flow of air and opposing reaction on the control volume, by Newtons trinity law. 1 This experiment will determine drag draw ins experienced by a NACA 0015 airfoil, subjected to a constant time out velocity at various baffle settings with varying angles of att ack.DATA ANALYSIS, THEORATICAL BACKGROUND AND PROCEDURE Apparatus in this experiment as shown in the figure 2, consisted of a small subsonic wind tunnel. The wind tunnel had an uptake cross-section of 2304 in2 and an effect crosses section of 324 in2. A large compressor forced air from room) into the inlet through the outlet tunnel and back into the room. This creates a steady flow of air and a recounting high velocity can be achieved in the test section. Instrumentation on the wind tunnel consisted of an inclined manometer and a pitot-static tube in the test section withal a manometer rake behind the tested objet (airfoil NACA 0015). The manometer rake consisted of 36 inclined manometers number 36 is used as a reference for the static pressure. all(a) other manometer measures the pressure behind the object in the airflow. Figure 2 Wind tunnel set up with instrumentation 5Before the experiment was performed the laboratory conditions were recorded, the room temperature was measur ed to be 22. 5 C (295. 65) and the atmospheric pressure 29. 49 inHg (99853. 14Pa). Theory The setup of this experiment includes a NACA 0015 airfoil placed in the wind tunnel. Considering the cross-sectional ambit A1, velocity V1, and the density of air p1 at the inlet and similarly the cross-sectional field of battle A2, velocity V2, and the density of air p2 at the outlet and by assuming that no mass is muddled amid the inlet-outlet section, we get the mass conservation comparison, p1 V1 A1 = p2 V2 A2 (1).Further, the airflow can be assumed to be incompressible for this experiment due to low velocity, the equation (1) can be reduced to V1 A1 = V2 A2 (2), more(prenominal)over, the air is assumed to be inviscid, the Bernoullis equation, p1+12? V12=p2+12? V22 (3) and the equation (2) can be reduced to Vth=2(p1-p2)/? 1-A2A12 (4) in order to square off the theoretical velocity. The pitot static tube is used to calculate the actual velocity of the flow by using, Vact= 2(p2-p1)? (5). Furthermore, the velocity coefficient can be mensural using, Cv=VactVth (6).The pressure and shear stress acting on the NACA 0015 airfoil produces a resultant force R, which according to the Newtons third law produces an equal and icy reaction force. For this experiment, in the condition of lower range of subsonic velocity, it can be assumed that pressure and density will be constant over the airfoil thus, D=jj+1? (uo2-ui2)dy=-12? uj2+uj+12o-uj2+uj+12iyj+1-yj (7) can be used to calculate the drag and, CD=Drag12(? air*Velocity2*area) (8) can be used for calculating the coefficient of drag. bit Part 1, Variation of inlet cross sectionIn this first part we recorded the pressure behavior in the test section by decreasing the inlet area. After the safety book of instructions were given by the TA and a chart for the readings prepared on the white board the wind tunnel was moody on. Two students were taking readings simultaneously from the inclined manometer in the test section a nd the static pitot tube, the readings were recorded in table 1. Between each reading the compressor was turned off due to the sullen level, it was important to give the compressor some time after each start up to have the corresponding conditions as in the previous measurement.Part 2, recording the wake profile of NACA 0015 For this part of the experiment the inlet area was fully opened and the airfoil first set to an angle of attack of 10, the wind tunnel was turned on and all 36 readings recorded (table 2) from the manometer rake. The measurement was repeated for an angle of attack of 15 and 20. RESULTS AND word of honor The linear relationship between the V actual and the V theoretical approves of the theory that the velocity coefficient, Cv can be used as a correction factor for the theoretical velocity. This is further demonstrated in (Graph2). The calculated results are shown in table 1.The approximated literature values of the coefficient of drag for NACA 0015 airfoil wer e obtained from a NASA published report 3 for the 10o AoA, the percent relative error is 3. 1%, for 15o AoA, the percent relative error is 31. 0%, and for the 20o AoA, the percent relative error is 38. 7%. Increases in angle of attack lead to a more disturbed airflow behind the wing section. This disturbed airflow created more drag, these drag forces were clearly discernable in table 3, 4. The angle of attack can be increased until the total drag forces choke larger than the resultant lift- force a wing is then no longer effective and stalls.The calculated drag forces are shown in tables 2-4. According to NASA, in their published report of Active flow control at low Reynolds numbers on a NACA 0015 airfoil, its is suggested that, by positioning the wake rake most 4. 5 times chord length behind wing to survey the wake. Further, two pressure orifices on opposite tunnel walls, aligned with the wake rake can be used to determine the comely wake static pressure. This type of wake rake enables the wake to be surveyed with only a few moves of the wake rake, hence improving the measurements of drag using wake rake. 2 At large angles of attack, the upstream velocity of the airfoil can no longer be considered as the free-stream velocity, largely due to the miniature sizing of the wind tunnel relative to the NACA 0015 airfoil hence, the assumption that the uo max > ui is valid for this experiment.CONCLUSION Ergo, it is evidently seen in the graphs 1 and 2 that, the averaged velocity coefficient, Cv, 1. 063 can be used as the correction factor for the theoretical velocity. Further, the consummate (4-32) drag forces were calculated to be 2. 72 N, 13. 46 N, and 46. 4 N for the following angles of attack, 10o, 15o, and 20o. Moreover, the drag coefficient were also calculated based on the observed data and than were directly compared with the literature values. For the 10o of angle of attack, the percent relative error was precise minimal at 3. 1% however the drag coef ficients for the 150 and the 20o were not very accurate, with the percent relative error of 31. 0% and 38. 7% respectively. This can be improved by implementing a smaller airfoil, so that the proportion of the wind tunnel covered by the airfoil is significantly smaller.Also, the jumble friction losses along the edges of the wind tunnel may very well be taken into the account to achieve greater accuracy. Finally, it can be concluded that, as the angle of attack of the airfoil increases, the drag force will also increase due to the effect of flow separation. REFERENCES 1 Walsh, P. , Karpynczyk, J. , AER 504 Aerodynamics laboratory Manual Department of Aerospace Engineering, 2011 2 Hannon, J. (n. d. ). Active flow control at low reynolds numbers on a naca 0015 airfoil. Retrieved from http//ntrs. nasa. gov/archive/nasa/casi. ntrs. nasa. gov/20080033674_2008033642. pdf 3 Klimas, P.C. (1981, March). Aerodynamic characteristics of seven symmetrical airfoil section through 180-degree ang le of attack for use in aerodynamic analysis of vertical axis wind turbines. Retrieved from http//prod. sandia. gov/techlib/access-control. cgi/1980/802114. pdf 4 Baals, D. D. (1981). Wind tunnels of nasa. (1st ed. , pp. 9-88). National Aeronautics And position Administration. 5Fig. 1, Wind tunnel set up with instrumentation, created by authors, 2012 APPENDIX stress Calculations Note AoA = ANGLE OF ATTACK. Sample calculations part 1, Baffle opening 5/5 Conversion inH2O to Pa (N/m2) 1 inH2O=248. 2 Pa (at 1atm) ?2inH2O ? 248. 82 PainH2O=497. 64 Pa Theoretical velocity Equation (4) Vth=2(p1-p2)/? 1-A2A12 , where p1-p2=497. 64 Pa, A2=2304 in2, A1=324 in2, ? Density air (ideal fluff law) laboratory conditions 22. 5 C (295. 65K), 29. 49 inHg (99853. 14Pa) ? =pRT=99853. 14Pa287JkgK(295. 65K)? 1. 1768 kgm3 ?Vth=2(497. 64pa)/1. 1768kgm31-2304 in2324 in22=29. 37m/s Actual velocity Equation (5)Vact= 2(p2-p1)? where p1-p2=522. 52 Pa, ? =1. 1768 kgm3 ? Vact= 2(522. 52Pa)1. 1768 kgm3=29. 80 m/ s Velocity coefficient Equation (6) Cv=VactVth=29. 8029. 37=1. 015 Sample Calculations Part 2, Angle of attack 10o, tube 1For dL, tube number 36 served as a reference pressure for all readings 26. 4cm 9. 2cm = 17. 2cm or 0. 172m Pressure difference, equation (7) ?p=SG*? H2O*g*L*sin? =1* light speed0kgm3*9. 81ms2*0. 172m*sin20o=577. 06 Pa Velocity, equation (8) note pressure difference previously calculated V1=2*SG*? H2O*g*L*sin air=2*577. 06 Pa1. 1768kgm3=31. 32 m/s Drag force, equation (9), for ui a velocity off from the tunnel wall was chosen to achieve a more realistic drag force D=jj+1? (uo2-ui2)dy=-12? uj2+uj+12o-uj2+uj+12iyj+1-yj=-121. 1768kgm3(31. 32ms)2+( 31. 5ms)2o-2(31. 5m/s)2i0. 01m=0. 07 N Total drag force, summation lead toDtotal = 9. 04 N, however due to the boundary layer along the inner walls of the wind tunnel a more accurate summation is the sum of the values of tubes 4-32 which results in a total drag force of 2. 72 N. Coefficient of Drag Equation (9), for the drag force the more accurate summation of tube 4-32 was used CD=Drag12(? air*Velocity2*area)=2. 72N12(1. 1768kgm3*31. 50ms2*(0. 1524m*1. 00m)=0. 031 To compare the Cd to a value found in literature the Reynolds number is required Re=? air*V*cViscosity=1. 1768kgm3*31. 50 m/s*0. 1524m1. 789*10-5kgs*m=315782. 35 Observation and Results for Part 1Table 1, Observations/Results part 1 Baffle curtain raising Inclined Manometer (inH2O) Pa ( x 248. 82 Pa/inH2O) Pitot Static (inH2O) Pa ( x 248. 82 Pa/inH2O) V theoretical (m/s) V actual (m/s) Cv 55 2. 00 497. 640 2. 10 522. 52 29. 37 29. 80 1. 015 45 1. 80 447. 876 1. 90 472. 75 27. 87 28. 35 1. 017 35 1. 15 286. 143 1. 25 311. 02 22. 27 22. 99 1. 032 25 0. 45 111. 969 0. 46 114. 46 13. 93 13. 95 1. 001 15 0. 05 12. 441 0. 08 19. 905 4. 64 5. 82 1. 252 Table 1 The theoretical velocity was calculated using the eq. (4) and the actual velocity was calculated using the eq. 5) from the obtained pressure data from the hand held pitot tube. The velo city coefficient, Cv, was calculated using the eq. (6). Note The sample calculations are given in the appendix section of this report. Graph 1 The results from Table 1 were used to create the plot of V actual Vs. V theoretical. Graph 2 The plot of the velocity coefficient and the actual velocity. From the plot, it can be clearly seen the very minute difference between the velocity coefficient values. Observation and Results for Part 2 Table 2, Observations/Recordings part 2, Angle of attack 10 liquified length in tube (. 1cm), drop 20Tube Nr. L (cm) dL (cm) Pressure (Pa) u (m/s) Drag force (N) 1 9. 2 0. 07 0. 07 0. 07 0. 07 2 9. 0 0. 00 0. 00 0. 00 0. 00 3 9. 0 0. 00 0. 00 0. 00 0. 00 4 9. 0 -0. 07 -0. 07 -0. 07 -0. 07 5 8. 8 -0. 13 -0. 13 -0. 13 -0. 13 6 8. 8 -0. 13 -0. 13 -0. 13 -0. 13 7 8. 8 -0. 07 -0. 07 -0. 07 -0. 07 8 9. 0 0. 00 0. 00 0. 00 0. 00 9 9. 0 0. 00 0. 00 0. 00 0. 00 10 9. 0 -0. 03 -0. 03 -0. 03 -0. 03 11 8. 9 -0. 03 -0. 03 -0. 03 -0. 03 12 9. 0 -0. 03 -0. 03 -0. 03 -0. 03 13 8. 9 -0. 07 -0. 07 -0. 07 -0. 07 14 8. 9 0. 64 0. 64 0. 64 0. 64 5 11. 0 1. 68 1. 68 1. 68 1. 68 16 12. 0 1. 01 1. 01 1. 01 1. 01 17 9. 0 -0. 03 -0. 03 -0. 03 -0. 03 18 8. 9 -0. 03 -0. 03 -0. 03 -0. 03 19 9. 0 0. 00 0. 00 0. 00 0. 00 20 9. 0 0. 00 0. 00 0. 00 0. 00 21 9. 0 -0. 03 -0. 03 -0. 03 -0. 03 22 8. 9 -0. 07 -0. 07 -0. 07 -0. 07 23 8. 9 -0. 07 -0. 07 -0. 07 -0. 07 24 8. 9 -0. 10 -0. 10 -0. 10 -0. 10 25 8. 8 -0. 10 -0. 10 -0. 10 -0. 10 26 8. 9 -0. 03 -0. 03 -0. 03 -0. 03 27 9. 0 0. 00 0. 00 0. 00 0. 00 28 9. 0 0. 00 0. 00 0. 00 0. 00 29 9. 0 0. 00 0. 00 0. 00 0. 00 30 9. 0 0. 00 0. 00 0. 0 0. 00 31 9. 0 0. 07 0. 07 0. 07 0. 07 32 9. 2 0. 34 0. 34 0. 34 0. 34 33 9. 8 0. 34 0. 34 0. 34 0. 34 34 9. 2 0. 07 0. 07 0. 07 0. 07 35 9. 0 5. 84 5. 84 5. 84 5. 84 36 26. 4 0 Reference 0. 00 0. 00 Total drag force (1-35) 9. 04 Total drag force (4-32) 2. 72 Coefficient of drag calculated 0. 031 Coefficient of drag literature 0. 030 Table 3, Observations/Recordings part 2, Angl e of attack 15 smooth-spoken length in tube (. 1cm), Inclination 20 Tube Nr. L (cm) dL (cm) Pressure (Pa) u (m/s) Drag force (N) 1 8. 2 0. 06 0. 06 0. 06 0. 06 2 8 -0. 01 -0. 01 -0. 1 -0. 01 3 8 -0. 01 -0. 01 -0. 01 -0. 01 4 8 -0. 04 -0. 04 -0. 04 -0. 04 5 7. 9 -0. 08 -0. 08 -0. 08 -0. 08 6 7. 9 -0. 04 -0. 04 -0. 04 -0. 04 7 8 -0. 01 -0. 01 -0. 01 -0. 01 8 8 -0. 01 -0. 01 -0. 01 -0. 01 9 8 0. 19 0. 19 0. 19 0. 19 10 8. 6 0. 49 0. 49 0. 49 0. 49 11 8. 9 0. 49 0. 49 0. 49 0. 49 12 8. 6 0. 39 0. 39 0. 39 0. 39 13 8. 6 0. 56 0. 56 0. 56 0. 56 14 9. 1 1. 40 1. 40 1. 40 1. 40 15 11. 1 2. 51 2. 51 2. 51 2. 51 16 12. 4 2. 74 2. 74 2. 74 2. 74 17 11. 8 2. 40 2. 40 2. 40 2. 40 18 11. 4 2. 00 2. 00 2. 00 2. 00 9 10. 6 1. 47 1. 47 1. 47 1. 47 20 9. 8 1. 06 1. 06 1. 06 1. 06 21 9. 4 0. 79 0. 79 0. 79 0. 79 22 9 0. 63 0. 63 0. 63 0. 63 23 8. 9 0. 49 0. 49 0. 49 0. 49 24 8. 6 0. 39 0. 39 0. 39 0. 39 25 8. 6 0. 32 0. 32 0. 32 0. 32 26 8. 4 0. 26 0. 26 0. 26 0. 26 27 8. 4 0. 26 0. 26 0. 26 0. 26 28 8. 4 0. 26 0. 26 0. 26 0. 26 29 8. 4 0. 26 0. 26 0. 26 0. 26 30 8. 4 0. 26 0. 26 0. 26 0. 26 31 8. 4 0. 26 0. 26 0. 26 0. 26 32 8. 4 0. 32 0. 32 0. 32 0. 32 33 8. 6 0. 56 0. 56 0. 56 0. 56 34 9. 1 0. 56 0. 56 0. 56 0. 56 35 8. 6 6. 30 6. 0 6. 30 6. 30 36 26. 2 0. 00 Reference 0. 00 0. 00 Total drag force (1-35) 19. 55 Total drag force (4-32) 13. 46 Coefficient of drag calculated 0. 145 Coefficient of drag literature 0. 100 Table 4, Observations/Recordings part 2, Angle of attack 20 Fluid length in tube (. 1cm), Inclination 20 Tube Nr. L (cm) dL (cm) Pressure (Pa) u (m/s) Drag force (N) 1 8 0. 16 0. 16 0. 16 0. 16 2 7. 6 0. 03 0. 03 0. 03 0. 03 3 7. 6 0. 03 0. 03 0. 03 0. 03 4 7. 6 0. 03 0. 03 0. 03 0. 03 5 7. 6 0. 03 0. 03 0. 03 0. 03 6 7. 6 0. 03 0. 03 0. 03 0. 03 7 7. 6 0. 03 0. 3 0. 03 0. 03 8 7. 6 0. 09 0. 09 0. 09 0. 09 9 7. 8 0. 16 0. 16 0. 16 0. 16 10 7. 8 0. 23 0. 23 0. 23 0. 23 11 8 0. 50 0. 50 0. 50 0. 50 12 8. 6 1. 17 1. 17 1. 17 1. 17 13 10 2. 37 2. 37 2. 37 2. 37 1 4 12. 2 3. 58 3. 58 3. 58 3. 58 15 13. 6 5. 39 5. 39 5. 39 5. 39 16 17. 6 7. 21 7. 21 7. 21 7. 21 17 19 7. 88 7. 88 7. 88 7. 88 18 19. 6 7. 88 7. 88 7. 88 7. 88 19 19 7. 04 7. 04 7. 04 7. 04 20 17. 1 5. 73 5. 73 5. 73 5. 73 21 15. 1 4. 09 4. 09 4. 09 4. 09 22 12. 2 2. 44 2. 44 2. 44 2. 44 23 10. 2 1. 37 1. 37 1. 37 1. 37 4 9 0. 66 0. 66 0. 66 0. 66 25 8. 1 0. 29 0. 29 0. 29 0. 29 26 7. 9 0. 23 0. 23 0. 23 0. 23 27 7. 9 0. 23 0. 23 0. 23 0. 23 28 7. 9 0. 19 0. 19 0. 19 0. 19 29 7. 8 0. 19 0. 19 0. 19 0. 19 30 7. 9 0. 19 0. 19 0. 19 0. 19 31 7. 8 0. 19 0. 19 0. 19 0. 19 32 7. 9 0. 46 0. 46 0. 46 0. 46 33 8. 6 0. 50 0. 50 0. 50 0. 50 34 8 0. 29 0. 29 0. 29 0. 29 35 8 6. 40 6. 40 6. 40 6. 40 36 26. 2 0 0. 00 0. 00 0. 00 Total drag force (1-35) 51. 30 Total drag force (4-32) 46. 64 Coefficient of drag calculated 0. 489 Coefficient of drag literature 0. 300